The present invention relates generally to the field of communication and power transmission, and in particular to wireless communication and power transmission through a barrier using ultrasonic waves.
Published patent application US2010/0027379, published Feb. 4, 2010 and incorporated herein by reference, discloses an ULTRASONIC THROUGH-WALL COMMUNICATION (UTWC) SYSTEM for communicating digital information through a barrier in the form of a thick metal wall, using ultrasonic techniques so that no through-holes are needed in the barrier. Using this system, signals can be transmitted through the barrier. For example, sensor signals that monitor conditions on one side of the barrier, can be transmitted to the other side of the barrier. The barrier may be the wall of a pressure vessel and the conditions to be monitored may be those of a hostile, high temperature and high pressure, gaseous or liquid environment in the pressure vessel.
U.S. Pat. No. 7,902,943 to Sherrit et al. discloses a WIRELESS ACOUSTIC-ELECTRIC FEED-THROUGH FOR POWER AND SIGNAL TRANSMISSION including a first piezoelectric transducer to generate acoustic energy in response to electrical energy from a source and a second piezoelectric transducer to convert the received acoustic energy to electrical energy used by a load.
U.S. Pat. No. 7,894,306 to Martin et al. for an APPARATUS AND METHOD FOR DATA TRANSFER THROUGH A SUBSTRATE discloses transferring data through a submarine hull or other solid boundary using high frequency acoustic signals to avoid penetration of the hull or boundary.
U.S. Pat. No. 5,594,705 to Connor et al. for an ACOUSTIC TRANSFORMER WITH NON-PIEZOELECTRIC CORE uses a transformer for transmitting energy across a medium, including primary and secondary transducers on opposite sides of a medium and a generator coupled to the primary transducer for applying a driving signal thereto.
U.S. Pat. No. 5,982,297 to Welle discloses an ultrasonic data communication system includes first and second transducers coupled together through a coupling medium for communicating input and output undulating pressure waves between the transducers for the transfer of input and output data between an external controller and an embedded sensory and actuating unit. An internal processor powers the second embedded transducer to generate ultrasonic waves into the medium that are modulated to send the data from the embedded sensor so that considerable energy is needed for the embedded circuits.
Also see U.S. Pat. Nos. 6,625,084; 6,639,872; 7,514,844; 7,525,398 and 7,586,392 for other approaches to the transmission of data or power through a barrier using ultrasound.
A more comprehensive approach to wireless data and power transmission through a barrier is taught by R. Primerano in “High Bit-rate Digital Communication through Metal Channels,” PhD dissertation, Drexel University, July 2010, hereafter referred to as Primerano. Without conceding that Primerano is prior art to the invention disclosed in the present application, Primerano is interesting because both he and the invention of the present application use Orthogonal Frequency-Division Multiplexing or OFDM modulation with a cyclic prefix to send data at a high rate through a metal wall using ultrasound. The use of OFDM compensates for signal loss due to echos caused by boundaries or due to other incongruities across the channel. Primerano does not, however, teach a system that simultaneously delivers power in one direction while data is transmitted in one or both directions, nor the elimination of certain, data-carrying, OFDM sub-carrier frequencies, which become contaminated by the power signal's harmonic signature.
A significant issue with simultaneously sending power and data is that the power delivery signal must be large to enable the delivery of a significant amount of power while the communication signals should be small to minimize the amount of power required for communications. As a result it can be difficult to avoid having the power delivery signal interfere with the communication signals. Using separate frequency ranges for the power signal and the communication signals can help minimize interference but the fact that the system is not strictly linear, i.e. the power amplifier, transducers and/or metal wall channel will create harmonics of the power signal, results in the generation of harmonics of the power delivery signal that can interfere with the communication signals.
As will be explained in the following, the invention disclosed here synchronizes the power delivery and communication signals such that the harmonics of the power delivery signal occur precisely at frequencies that coincide with individual channel frequencies of the OFDM signal. This results in a far more effective transmission of data and power through a barrier, than has been possible in the past.